C1-C4-Oxygenates, for example methanol, formaldehyde, acrolein, acrylic acid, are important products of the chemical industry.
Such C1-C4-oxygenates are typically not obtained on the industrial scale by direct partial oxidation of corresponding saturated hydrocarbons, but rather by an indirect route via intermediates. For example, C1-oxygenates such as methanol or formaldehyde are obtained indirectly from methane. In this case, methane is first reacted with steam and oxygen to give synthesis gas, which is subsequently converted at relatively high pressures catalytically to methanol. The methanol can optionally be oxidized to formaldehyde in a further process.
A direct reaction of C1-C4-alkanes, preferably of methane, with oxygen or oxygenous gases to give the desired C1-C4-oxygenates would be much simpler and therefore highly attractive from an economic point of view.
The direct reaction of methane with oxygen or oxygenous gases to give C1-oxygenates is of the greatest industrial interest according to the current state of knowledge. It is known and described in many scientific publications and in the patent literature, for example in K. Tabata et al., Catalysis Reviews 2002, volume 44(1), pages 1 to 58, especially pages 1 to 25. This reaction can be performed in the presence of catalysts or without catalysts.
In summary, however, the processes for preparing methanol from methane by direct partial oxidation of the methane, described in the prior art, have at least one of the following disadvantages:                a) in order to achieve a high methanol selectivity in the direct partial oxidation of methane to methanol, only a very small portion of a large amount of methane is converted to methanol; the unconverted amount of methane is recycled back into the oxidation reactor (“cycle gas process”). This is technically complex and not very economic since further process operations, such as compression, etc., firstly have to be carried out. Moreover, there may be enrichment of undesired secondary components or even undesired side reactions.        b) When the direct partial oxidation of methane to methanol is performed with high conversion of methane, the methanol selectivity is reduced, i.e. too high a level of undesired by-products form, which have to be removed again in a technically complex manner and hence impair the economic viability of such processes.        c) The use of aggressive or corrosive assistants, such as SO3, NOx or halogen compounds, is technically complex.        d) Multistage reaction regimes require, inter alia, multiple reactors or reaction steps.        